The surface of Jupiter’s icy moon Europa may hide oceans of salty, Earth-like ocean water, say astronomers. According to New Scientist magazine, a fresh study of the sixth largest moon of the gas giant Jupiter revealed that its frozen surface is covered with formations of magnesium salts, the best evidence so far to back scientists’ theory that liquid can seep from beneath the ice to the surface, giving observers a glimpse into the composition of the moon’s liquid depths.

California Institute of Technology astronomer Mike Brown, famously known as the man who declared that Pluto isn’t a planet after all, used the telescope at Hawaii’s W. M. Keck Observatory to take a look at the light reflected off of Europa in order to analyze the chemical composition of its surface. He was able to use his findings to supplement what astronomers learned about Europa when the Galileo satellite orbited Jupiter from 1995 to 2003 and see what the satellite missed, the presence of magnesium sulfate.

Europa is tidally locked, which means that one side of the sphere always faces Jupiter. Magnesium only shows up on the part of the moon that is exposed to radiation from Jupiter and material ejected by Jupiter’s other moon, Io. Brown and NASA Jet Propulsion Laboratory scientist Kevin Hand believe that the magnesium is coming from another source, inside Europa.

“We think the ice shell of Europa is serving as a window into the ocean below,” said Hand. “Europa likely has a sea salt composition similar to our own ocean.”

Galileo spotted dark spots littering Europa’s icy surface. Some scientists thought the dark spots were magnesium, but others argued that the moon is constantly being bathed in sulphur thrown off by Io, and that the dark spots are sulphuric acid.

“There’s been this long-raging debate about whether the dark material on Europa is salts from the salty ocean below, or sulphuric acid from radiation,” Hand said.

Hand and Brown believe that magnesium is being transported to the surface of Europa by upwellings of water from below the ice. A prime candidate for the upwelling substance is magnesium chloride, which would indicate that the water below the surface is dominated by chlorine salts like sodium chloride and potassium chloride, making that water favorable for life.

Cynthia Phillips of the SETI Institute in Mountain View, California told New Scientist that Brown and Hand’s argument is reasonable, and that “Chlorine salts are better for life as we know it.”

Hand said that he isn’t content to observe and speculate from this far away, however.

“If we could just send a spacecraft out there to inspect the surface in much greater detail, we might be able to detect salts and maybe even organic compounds or possible indicators of life in Europa’s liquid water ocean.”

The nearest possible Europa exploration mission will come in 2022 when NASA launches the Jupiter Icy Moon Explorer, also known as “Juice.” That mission will send a satellite to Europa, as well as its neighbor moons, Callisto and Ganymede.